The subject matter disclosed herein relates to eddy current probes, in particular, to an eddy current probe useable over a wide range of frequencies.
Eddy current probes are a form of nondestructive testing devices that can be used to inspect test objects, such as tubes or pipes, to detect and analyze defects in the objects. Nondestructive testing allows an inspection technician to maneuver an eddy current probe through a test object in order to scan for defects.
In an eddy current probe, a magnetic field is used to induce an electrical current in the test object. The magnetic field is typically generated by one or two electrically conductive coils, or windings, in the probe. During operation of the probe an electrical current is sent through the coil, or coils, which generates a magnetic field that passes through the test object and induces an electrical current in the test object called an eddy current. The eddy current travels through a tube in a circular pathway along a circumference of the tube in a plane that is perpendicular to an axis of the tube.
If the induced eddy current passes through a flaw or defect in the test object, for example, erosion and pitting of the inside diameter of a tube, or if the inside diameter of the tube fluctuates as the probe travels through the tube, the induced eddy current is perturbed and the coils will detect this as a varying impedance. In response to detecting the varying impedance, the coils will generate electrical signals that represent physical characteristics of the defect. By analyzing these electrical signals, various characteristics of the defect (e.g., location, size) can be determined. Each of the coils will detect a different impedance variance because the coils are located at a different distance from the defect. The impedance difference detected by the coils can be converted into a two-dimensional impedance data display.
Typical eddy current probes have a limited testing frequency range because the two coils in the probe are balanced in a wheatstone bridge configuration against fixed resistors. The fixed resistors are typically located in a remote test instrument.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.